Embodiments of the invention relate electric motors and, in particular, to controlling permanent magnet electric motors.
Permanent magnet motors typically have three windings on a stator and a permanent magnet on a rotor. The stator windings are typically powered from a three-phase converter that creates a balanced set of three phase currents. This arrangement of three stator windings powered by the three-phase current system generates a rotating field with a rotation speed proportional to the number of pole pairs and the frequency of the stator current. In a typical permanent magnet motor, the rotation speed of the rotor is determined by a speed sensor or derived from the signal from a position sensor. A rotor position sensor gives information about position of rotor magnets with respect to stator windings. The position of the rotor magnets is important for properly energizing stator windings with current to control torque.